Innovative gas monitoring with spacial and temporal analysis

ABSTRACT

The present invention relates to the monitoring of gas concentrations possible in very low ranges (i.e. low ppb and even ppt ranges) and especially use thereof in environmental monitoring, exposure assessment, bomb detection, and health studies. The invention can use a spatial and temporal assessment of gas concentrations that enables the sources of the gas in question to be located and identified which is useful in environmental and health field but can also be applied to other fields an example of which is detecting and locating explosives. This technology can uses small, light weight, and low power components that allow for the monitor to be portable and even worn on a person as a personal monitor. This technology can be used in stationary monitors as well.

CROSS REFERENCE TO RELATED APPLICATIONS

I am filing a non-provisional application claiming the benefit of theprovisional application that is No. 60/481,266 and was filed Aug. 20,2003.

DETAILED DESCRIPTION

The present invention relates to the monitoring of gas concentrationspossible in very low ranges (i.e. low ppb and even ppt ranges) andespecially use thereof in environmental monitoring, exposure assessment,bomb detection, and health studies. The invention can use a spacial andtemporal assessment of gas concentrations that enables the sources ofthe gas in question to be located and identified which is useful inenvironmental and health field but can also be applied to other fieldsan example of which is detecting and locating explosives. Thistechnology uses small, light weight, and low power components that allowfor the monitor to be portable and even worn on a person as a personalmonitor. This technology can be used in stationary monitors as well.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the accompanying drawings which show, byway of example, embodiments according to the present invention and inwhich;

FIG. 1 shows in graphical form exemplary data collected over a three dayperiod;

FIG. 2 shows in graphical form data corrected for sensor baselineresponse and overlaid on the data of FIG. 1;

FIG. 3 shows in graphical form data corrected for changing sensorsensitivity over time;

FIG. 4 shows in graphical form monitor predictions when multiple sensorsare averaged;

FIG. 5 shows a plot of percent relative standard deviation versus H2Sconcentration;

FIG. 6 shows a plot of the output of five sensors working in asynchronized mode of operation;

FIG. 7 shows a plot of a sample cycle for one sensor exposed to H2S;

FIG. 8 shows a plot of a sample cycle for a sensor exposed to anotherconcentration of H2S;

FIG. 9 shows a plot of the comparison between the H2S filter mode andthe baseline calibration;

FIG. 10 shows a plot of logarithmic fitted curves for sensor outputs;

FIG. 11 shows in schematic form a monitor according to an embodiment;

FIG. 12 shows a plot of an exemplary measurement cycle;

FIG. 13 shows a plot of another exemplary measurement cycle;

FIG. 14 shows in graphical form an exemplary three dimensional plot formeasurements;

FIG. 15 shows in graphical form another exemplary three dimensionalplot;

FIG. 16 shows in graphical form another exemplary three dimensionalplot; and

FIG. 17 shows an exemplary arrangement for a sensor array and sourcelocation method according to an embodiment.

This technology is a platform that can be tuned and adjusted to measuremany different gases including but not limited to H2S, ammonia, SO2,NO2, and others even compounds that are related to explosives.

This personal or portable monitor can include a device that tracksspacial position for example a GPS device or a tracking system thatworks based on a receiver receiving a signal from stationarytransmitters of known location and triangulating the position of themonitor based on the signals received.

This monitor will include a means to record and store the gasconcentration, special position and time of the readings. This monitorcan be fitted with the provision to transmit the data collected eitherby a wire connection or a wireless transmitter to a computer station orother similar device. The data can then be stored and archived andanalyzed using algorithms designed to watch and notify if conditions ofconcern arise. These algorithms can include spacial and temporalanalysis of the gas concentrations (in effect mapping of the gasconcentration) that may provide evidence of the sources of the gasesbeing measured (i.e. locate the sources).

Several monitors can be downloading (by wireless transmissions ifneeded) to a single database that is updated and maintained with thealgorithms applied to constantly compare the new data to previouslycollected data and watch for anomalies that can identify undesirableconditions. For example, multiple mobile monitors can measure andtransmit concentration and position information to a central computerwhich combines and analyzes the information and can characterise the gasconcentrations over an area that is useful for exposure, environmentaland health concerns. The information can also identify and locatesources of the gas in question which is valuable in trying to reduce theconcentration of the gases by locating and eliminating the source. Forexample this would be useful in industrial operations were some fugitiveemission of gases go unnoticed by the standard air monitoring networks.This method would be useful in many other fields including the detectionand locating of explosive devices within apartment buildings or outdoorenvironments including public areas.

The work done to prove the concept of this invention is in two majorareas, first the gas monitor, and secondly the spacial temporal gasconcentration analysis.

The following is a description of a monitor that uses electrochemicalcells that have a low noise to signal ration which makes them verysensitive. The cells used in the prototype are made by TSI but othersimilarly sensitive cells would work the same. The prototype was tunedto and tested on H2S gas but it can be tuned to measure other gases. Thepresent prototype superimposed a gas concentration of the target gas onthe sensors and generates this gas using electrochemical cells (made byACD) but could use other electrochemical cells or methods to generatethe gas on the monitor.

The super imposed gas does not have to be the same as the gas to bemeasured. A different gas could be used to react with and eliminated theeffect of an interfering gas, or react with the target gas and form adifferent compound which is then measured on the sensitive sensors.Similarly a different gas could be introduced into the sample streamthat forms a compound on the surface of the sensors that that will reactmore readily with the target gas and provide a stronger signal. Ineffect, the superimposed gas can be used to isolate or amplify thesignal from the target gas.

The development of the invention has used three prototypes (threephases) to prove the concept of measuring low concentration of gases ona small light weight monitor that could be portable or personally worn.This development has targeted H2S and other reduced sulphur compoundsbut the same methods could be used to measure other gases. The followingdescribes the development. It is possible to replace individualcomponents of these prototypes with other things not mentioned thatperform the same function.

The methodology was developed to monitor low ppb (parts per billion) airconcentrations of H2S in real time with small light weight equipmentadaptable to portable or even personal monitors.

In the first phase an investigation of monitoring techniques determinedthat highly sensitive electrochemical sensors (amperametric sensor) werethe most promising technique given their small size and low powerrequirements.

The difficulties with the electrochemical sensors are that they respondto many compounds (lack of selectivity) and the response to low ppblevels of H2S is not consistent. While they are sensitive enough torespond to 1 ppb H2S the response is not consistent and varies withhumidity, sensor baseline, and recent exposures to H2S. The sensorresponds to H2S concentrations with a measurable increase in currentthat rises logarithmically requiring hours to reach to a stable outputand similar time to return to the pre exposure baseline levels. Duringthis logarithmic increase or decrease in current measured the sensorsensitivity to H2S changes making it difficult to predict H2Sconcentrations.

The methodology developed incorporated the following techniques toaddress the complicating factors: Impose bias voltage (+300 mv) onsensor to reduce sensor response to other reactive gases (phase 1)Frequent Baseline correction (phase 1), Frequent calibration cycles (tomeasure sensor sensitivity) (phase 1), Using multiple sensors to improveaccuracy and eliminate outliners (phase 1) Superimposed H2Sconcentration on the sample (to maintain sensor sensitivity) (phase 2)Gas specific filters to further isolate the sensor's response to H2S(phase 2) Logarithmic curve fitting to measure sensor response (phase 2)The first phase of the investigation used a prototype monitor with thecapability to adjust bias voltage, baseline correct, sensitivitycorrect, and used multiple sensors. This prototype had limited datalogging capability only taking readings every ten seconds. The followinginformation was obtained from the investigation.

FIG. 1 shows data collected over three days comparing the H2Sconcentrations measured by a commercial ambient monitor versus aprototype monitor using electro-chemical sensors (calibrated with theaverage sensitivity over the time period). The figure shows that overallthe prototype monitors response is correlated with H2S concentrationsbut there are large errors for an individual measure. These errors aredue to the sensor sensitivity and baseline drifting during the sampleperiod.

FIG. 2 show data corrected for the sensor baseline response overlaidupon the raw data from FIG. 1. An estimate of the baseline was obtainedby periodically running the sample through a zero gas filter andmeasuring the sensor response. The figure shows there is a greatreduction in the scatter of the data particularly at the lowerconcentrations. There is still considerable error in the measurements atthe higher end of the scale.

FIG. 3 shows data that has been corrected for changing sensorsensitivity over time overlaid upon the previous data. There issignificant reduction in the error. Sensor sensitivity was determined byperiodically exposing the sensor to known concentrations of gas andrecording the response (basically recalibration).

FIG. 4 shows the improvements of the prototype monitors predictions whenmultiple sensors are averaged.

FIG. 5 plots the percent relative standard deviation (RSD, this is thestandard deviation of a group of data points at a given H2Sconcentration divided by the mean of those points) versus the H2Sconcentration. The figure shows the improvements in the prototypemonitors precision resulting from the application of the methodologiesdiscussed in this section. An estimate of the detection limit of themonitor is obtained by reading the H2S concentration when the fit linescross the 33% RSD (this is related to three standard deviation of theinstrument background noise which is a commonly used by laboratories asthe limit of detection). The detection limit of the prototype operatingwith baseline correction, sensitivity correction, and multiple sensorsis roughly 2 to 3 ppb.

In the second phase a second prototype was constructed with thefollowing improvements: 1 The capability to generate a H2S concentrationto superimpose on the sample 2.The capability to quickly change thesuperimposed H2S concentration for calibration purposes by adjusting theflow rate which increases the concentration of the superimposed H2Sconcentration which allows for a simple method to check sensorsensitivity providing a convenient calibration method 3. A record rateof three readings per secondThe monitor continuously cycles the sensorsthrough the following four modes of operation: 1 Baseline calibration 2Span calibration 3 Sample reading 4 Sample reading with an H2Sfiltercombining the information from the four modes provides a goodestimate of the H2S concentration as well as other reactive sulphurcompounds. The monitor has grouped the six onboard sensors into groupsof two and offset the modes of operation so that there is always a setof sensors reading a sample (maintaining a continuous monitor).

The following sections summarize the findings of the investigation ofthe second prototype.

FIG. 6 shows the output of five of the sensors working in synchronizedmodes of operation and being exposed to varying concentration of H2S andmethyl mercaptan (a common interfering gas that can also be detected bythe human nose at low concentrations). The figure shows the similarmagnitude of response between the sensors. This similarity in responseis a result of a 25 ppb superimposed H2S concentration that maintainsthe concentration of the secondary reaction products on the sensorsurface and provides similar sensor sensitivities.

The capability to quickly change the superimposed H2S concentration forcalibration purposes and the increased recording rate has enable themonitor to operate in short cycles that help to eliminate noise andallows for better interpretation of the sensor output. FIG. 7 is asample of a cycle for one sensor exposed to roughly 1 ppb of H2S. Themodes of the cycle are listed on the figure. Comparing the output duringthe sample modes and the H2S filter mode is an indication of theresponse to 1 ppb. Similarly in FIG. 8 the response to 8 ppb is shown.In FIG. 9 the comparison of the line during the H2S filter mode and thebaseline calibration is an indication of 15 ppb methyl mercaptan thatwas present along with 8 ppb H2S.

The cycles used here are examples of how they can be used to measure gasconcentrations. The ordering of the parts of the cycle can be changedand not all the parts of the cycle are required to measure the gasconcentration.

FIG. 10 demonstrates how logarithmic fitted curves will be used to fitto the output and compared to quantify sensor output. The first part ofthe figure is the sample mode while the second part is the H2S filtermode the arrow indicates the sensor response.

In the third phase the product is a monitor for H₂S that enablepersonal/portable monitoring with a low ppb detection limit. In additionto H₂S, the monitor also estimates a concentration of a group of otherreduced sulphur compounds (ORS) having odours that are sometimesmistaken for H₂S.

The monitor uses highly sensitive electrochemical sensors (also calledamperametric sensor) because of their small size and low powerrequirements. The difficulties with the electrochemical sensors are thatthey respond to many compounds (lack of selectivity) and the response tolow ppb levels of H2S is not consistent. While they are sensitive enoughto respond to 1 ppb H2S the response is not consistent and varies withhumidity, sensor baseline, and recent exposures to H2S. The sensorresponds to H2S concentrations with a measurable increase in currentthat rises logarithmically requiring hours to reach a stable output andsimilar time to return to the pre-exposure baseline levels. During thislogarithmic increase or decrease in current measured the sensorsensitivity to H2S changes making it difficult to predict H2Sconcentrations.

A methodology was developed to address the complicating factors usingthe following techniques: Imposed bias voltage (+300 mv) on sensor toreduce sensor response to other reactive gases Frequent Baselinecorrection Periodic calibration (to measure sensor sensitivity) Usingmultiple sensors to improve accuracy and eliminate outlinersSuperimposed H2S concentration on the sample (to maintain sensorsensitivity) Gas specific filters to further isolate the sensor'sresponse to H2S Logarithmic curve fitting to measure sensor response Theschematic diagram in FIG. 11 illustrates the layout of the componentsused to implement the methodology developed. The monitor uses twospecial electrochemical sensors with bias voltage adjustment on each ofthree channels. The valves on each channel switch rapidly (15 sec. to 5min.) between drawing an air sample; an air sample with the H₂S filteredout, or an air sample with all contaminants removed for a baselinereading. The H2S and ORS signals are calculated based on the differencein the sensor output between the different samples. Logarithmic curvefitting is use to quantify the differences in sensor output asillustrated in FIG. 10 for a sensor exposed to 1 ppb H2S. Low levels ofH₂S are generated in each channel and superimposed on the sample with acontrolled flow loop. Exit filters remove any H2S that has been addedbefore the air leaves the monitor. Because low humidity can damage thesensors a humidity module at the intake will increase moisture in thesample. A calibration module will be connected to the monitorperiodically to provide calibration. In between main calibrations, asensitivity check (quasi calibration) is possible by decreasing the flowwhich increases the superimposed H2S concentration by a known amount tothe sensors.

The methodology described above has been demonstrated in laboratory andfield test in a briefcase size prototype. The components (filters,manifolds, circuit boards) displayed in the prototype are much largerthan necessary and can be miniaturized so the size and power consumptionis suitable for a battery powered personal monitor. Laboratory testresults are shown in FIG. 12 for H.sub.2S levels of 0, 6, 12, and 24 PPBgenerated in a chamber in the laboratory. Note the changes inconcentration in the chamber were associated with the transition periodsshown in the figure and do not reflect the response time of the monitor.Data from ten days of field-tests where the prototype was collocatedwith an ambient monitor at an Alberta Environmental Protection stationis shown in FIG. 13. The field and laboratory test data shows goodagreement to the expected H.sub.2S, concentrations in the low ppb range.The field test data in FIG. 13 also shows predicted levels of the ORSpresent at the site.

The portable version of the monitor includes three channels providingcontinuous measurements of H.sub.2S, ORS, and baseline levels. Size andweight can be minimized in the personal monitor by using only onechannel, which would provide an intermittent measure of H2S and ORSrather than a continuous measure.

The unique aspects of low detection limit, light weight, and low poweroperation will compete with existing monitoring systems and open newmarkets in areas considered impractical at this time.

The portable monitors will allow government agencies to respond topublic complaints by taking measurements to determine the level of H₂Sand ORS. The personal monitor will provide information for healthassessments and could be used to provide concentration data for studiesthat look at the impact on human and animal life. Industries would alsobe interested in the monitors for the reasons above as well as thebenefits gained from collecting this air data with an addedspacial/temporal analysis which can locate sources of contamination.

Innovation in technology can precipitate profound changes in practicesand approaches to problems. Low ppb air quality monitoring has beencharacterized by permanent ambient monitoring stations that are costlyand lack flexibility in addressing public concerns about air quality andhealth. A portable/personal monitor with ambient monitor detectionlimits opens the possibility of answering the questions the public israising that are impractical to address with the current monitoringregime and provide valuable solution to other questions that industrieshaven't considered yet. With respect to the Spacial Temporal GasConcentration Analysis, the following is the proof of concept. A studyof PAH concentrations resulting from a coal fired household furnace isprovided to demonstrate the concept of locating sources using spacialand temporal gas concentration (although the PAH are fine particulatebounds they act as a gas for the purposes of this analysis in thisinstance).

A residence in Vegreville, Alberta was monitored over a five week periodfor outdoor air concentrations of PAHs and between Feb. 21 and Mar. 28,2003. Measurements of PAHs were taken using a real-time monitor (PAS2000 CE PAH monitor, Ecochem Analytics Inc.). The location of theresidence monitored was roughly 100 meters east of the location of thecoal fired furnace. Meteorological data was obtained from an EnvironmentCanada weather station located roughly 3 km from the residences.

A comparison between the real-time outdoor measures of PAHs and the windconditions at the time can provide insight into sources of emissions.Studies have shown that weak air movements or calm conditions overcities are correlated with poorer air quality due to pollution not beingeffectively dispersed. Where no significant point source of PAHs existsin the community or region, the highest concentration of PAHs occur atcalm or low wind speeds and the levels decrease to low background levelsat high wind speeds.

The real-time PAH and wind data was combined and plotted in FIG. 14which shows a surface representing the mean of the outdoor real-time PAHlevels versus wind speed and direction. The figure shows an increase inthe average PAH concentration at elevated wind speeds from the westerlydirection indicating a point source in the direction of the coal-firedfurnace. A plot of the average PAH levels versus wind direction andtemperature shows increased levels when the wind is from the west attemperatures below 15.degree. C. (see FIG. 15). This is as expectedgiven the coal furnace will be producing more heat and higher omissionat these low temperatures. Recharting the wind speed and directiondiagram using only data with temperature below 15.degree. C. in FIG. 16shows a dramatic increased impact of the coal furnace at coldertemperatures. These figures demonstrate that a point source existed inthe direction of the coal furnace and impacted the house monitored whenthe wind was above 10 km/hr in the direction spanning west-southwest tonorthwest at temperatures below 15.degree. C. The coal furnace wasresponsible for the increased PAH levels assuming there were no othersignificant point sources of products of incomplete combustion in thatdirection.

This demonstrates how directions of the point sources can be locatedwith real-time concentration data and wind speed and direction data. Ifdata were collected in many locations then the directions provided canbe used to pin point the sources location by over laying the directions.With moving monitors the data will be analyzed using a quasi finiteelement analysis with data from finite geographic areas grouped togetherand compared with wind speed and direction. Point sources will appear ineach finite element similar to the PAH surface in FIG. 16. Lines struckin the direction to a point source from the centroid of several finiteelements will cross at the location of the point source. Computeralgorithms will be created to perform these tasks on a continuous basisand will be able to determine if new point sources emerge and providealarms or warning of such.

Wind is not a consideration in indoor environments were concentrationdata will be mapped and areas of higher concentration will indicateproximity to sources. Temporal patterns of concentrations indoors canalso be used to identify sources.

This inventions application to explosive dectedtion as well as manyother area is demonstrated here. Sep. 13, 1999 at least 116 people arekilled when an eight-story Moscow apartment building is blown up by anexplosion. Sep. 9, 1999 an explosion collapses the middle of anine-story apartment building in a residential Moscow neighborhood,killing 93 people. In both of these cases large bombs were detonatedwithin the buildings. This type of attack could pose a significantthreat to America as foreign students or those posing as students couldcarry explosives in backpacks into apartment buildings unnoticed andbuild up a bomb weighing tons in a matter of weeks. This large bombcould be easily detonated by a cell phone call from anywhere.

Portable explosive detection devices carried by security personalwalking apartment hallways would be able to detect bomb-buildingactivity in the suites. Further, a number of these portable detectorscould wirelessly link to a central computer to provide a explosivesurveillance system. This system could provide long-term monitoring of abuilding for the presence of explosive devices or be used for one-timesweeps of a number of buildings. It could also provide surveillance forexplosive devices in public where it is difficult to screen peopleentering different areas.

This approach would locate explosives by identifying anomalies in airconcentration of an explosive indicator compound monitored over spaceand time. The system would compare concentration patterns from one areato another and would track changes in concentration patterns at onelocation over time. The system would use small portable gas detectionmonitors (with ultra low detection limits) carried by personnel. Themonitors would be tuned to detect a gas that is given off by explosivematerials and would transmit the data along with monitor position to acentral computer in real time. The central computer would compile thedata and generate a map of the characteristic concentrations of theindicator gas over the area in question-such as a large apartmentbuilding or public gathering place to be used as reference for futurereadings. The central computer would use powerful statistical algorithmsto analyze the incoming data and identify any spacial or temporalanomalies in the air concentrations that require additional monitorpasses or other appropriate responses to confirm the presence of anexplosive device.

The effectiveness of such an explosive surveillance system would belimited by the detection limit of the portable monitors. It is not clearwhat detection limit would be required but it could be in the part perbillion or trillion (ppb or ppt) range. A small portable air monitorwith this detection limit is not commercially available but it may bepossible to develop one.

An environmental issue being addressed by this concept is fugitiveemissions of natural gas. Fugitive natural gas leaks are a significantcontributor of green house gas (GHG) emissions and are responsible forgas losses estimated at roughly $200 million annually in Canada. A goalof this initiative is to develop a system that measures the amount offugitive emissions at a facility and localizes the major emissionsources within that facility using continuous point measures of methane.

The current approach to measuring overall fugitive natural gas emissionsat a facility involves open path optical sensing systems. These systemsuse a beam of light projected over a long distance (usually along thefacility boundary) to measure the air concentrations of natural gas andpredict the facility fugitive emission rate (see, for example, FIG. 17).Advanced systems can also locate individual plumes. Alberta ResearchCouncil (ARC) has demonstrated the Differential Absorption Lidar (DIAL)technology which can provide two and three dimensional pictures ofplumes at a facility boundary (Presentation to PTAC Air Issues Forum,Nov. 19, 2003. http://www.ptac.org/env/dl/envf0303p11.pdf).

The current approaches to localize fugitive emission sources usehand-held instruments that personnel carry through a facility eithermeasuring the size of leaks or looking for leaks. The size of a leak isdetermined by measuring natural gas concentrations in the immediatevicinity of the leak (i.e. sniffing a flange). Currently, leaks arelocated by sniffing all potential locations. Recent advances will seehand-held sensors (open path optical sensors or infrared cameras) thatcan be used to locate plumes from leaks several meters from the monitor.

These current methods use high-intensity data collection over a shortperiod of time and provide a snap shot of the fugitive emission at afacility. The innovation in the proposed technology will both localizefugitive sources and characterize overall site emissions in a continuousmanner using long-term, low intensity data collection combined withsophisticated data analysis.

The purpose of the new technology is to characterize overall facilityemissions and localize the sources of these emissions using pointmeasures combined with a sophisticated data analysis. This concept wouldresult in a continuous surveillance system that consists of a monitorfeeding data to a computer that updates a fugitive emission map of thefacility. The crux of the idea is that a sophisticated analysis ofcontinuous point measures is a more efficient and effective method tocharacterize and reduce fugitive emission than the current alternativesof short duration facility audits using systems like the DIAL laser orhandheld sensor carried by personnel.

The only other alternative that attempts to do both source localizationand overall site fugitive emission measures is the DIAL systemdemonstrated by ARC. The one DIAL system planned for Western Canadawould move between sites and provide snap shots of plume profiles at thefacility perimeter. The continuous nature of the proposed system is asignificant improvement over the DIAL system in that it will bettersupport continuous improvement strategies at facilities. Facilitymanagers and operators will have continuous feedback of the impactchanges in operational practices and procedures have on fugitiveemission which will be a powerful tool in continuous improvementstrategies.

If adequate resolution of leak location is achieved, the proposedtechnology could also be an alternative to the hand- held leak locationdevices currently in use. These hand-held systems depend on personnel tomove the monitor into the plume for measurement with the position of themonitor identifying the leak location. In contrast, the proposedtechnology relies on the wind to carry the plume from the leak locationto the monitor, which is stationary, and traces back to the location ofthe leak using computer algorithms to analyze the wind information.Again, the crux of this approach is that it will be more effective (andless expensive) to leave a monitor running in a fixed location and havea computer perform a complex analysis of the data than it is to havepersonnel move the monitor around with little analysis of the plume. Animportant advantage of the proposed system is that it performs acontinuous exhaustive surveillance of the entire facility where thehandmonitors only finds leaks where and when they are looked for,leaving leaks in unsuspected locations undetected. As a possiblelimitation, the proposed system will provide a continuous measure of theleakage rate from a building but will not likely be able to resolve leaklocation within the building.

The technologies current stage of development is a conceptual fieldprototype. The fundamental concepts of the technology have beendemonstrated in the field with other contaminants but have not beenattempted on natural gas. The fundamental concept of locatingcontaminant plumes with point measures has been demonstrated in previouswork identifying emissions from a coal fired furnace. The attached FIG.16 taken from an unpublished study by the applicant shows the averagelevels of point measures of PAH concentrations plotted with wind speedand direction. This figure represent five weeks of data taken from alocation near a house that was burning coal for heat. The contaminantplume shows up on the figure as a spike in concentration with wind fromthe west (the direction source) at 20 km/h. The figure shows how sourcescan be located using point measurements rather than open path opticalsensing systems. This same approach will be able to locate the plumes ofnatural gas fugitive emissions.

This project will determine the sensitivity (i.e. how small of a leakcan be located to what resolution) of the surveillance system.Additionally, the relationship between field monitor performance andsystem sensitivity will be determined (i.e. what quality of monitor doyou need to make an effective system).

The market potential for the technology is a surveillance system forevery gas plant. A surveillance system can be available soon after theproject is complete (or even before) if it uses commercially availablemonitors and manual data analysis (performed offsite). With experience,the data analysis will be streamlined and software will be developed tocompletely automate the analysis component of the system and provideon-site data analysis in real time. Given a sufficient market driver,the ideal surveillance system that uses a low maintenance monitor withon-site real time data analysis could be available in two years.

Traditional air dispersion modeling starts with a source of knowncharacter and predicts down-wind plume concentrations under assumedmeteorological conditions. This concept endeavors go in the oppositedirection by measuring plume concentrations and predicting sourcecharacteristics (location, size, etc.). Algorithms developed to solvethis puzzle can be readily applied to data collected at facilities toprovide valuable information to reduce fugitive emissions.

1. A method for determining an emission source, said method comprisingthe steps of: measuring concentrations of an emitted material at asingle measurement point; measuring changes in wind velocity over time;performing spatial temporal analysis of said concentration measurements;generating one or more wind vectors based on said measured changes inwind velocity; collating said measured concentrations with said windvectors to generate an emissions plot; and defining boundaries for oneor more plumes on said emissions plot wherein said one or more plumesare indicative of an emission source.
 2. The method as claimed in claim1, wherein said changes in wind velocity are measured independently ofsaid single measurement point.
 3. The method as claimed in claim 1,wherein said single measurement point comprises a single sensorpositioned any distance from a potential emission source.
 4. The methodas claimed in claim 2, further including the step of superimposing aknown emission concentration on said sensor during a monitoring cycle,so that sensitivity of said sensor is enhanced.
 5. A method fordetermining a source of an emission, said method comprising the stepsof: measuring concentrations of an emission at a single measurementpoint; measuring changes in wind velocity over time; performing spatialtemporal analysis of said concentration measurements; generating one ormore wind vectors based on said measured changes in wind velocity;generating a trajectory for the emission based on said measured emissionconcentrations and said wind vectors; projecting back along saidtrajectory and correlating one or more points along said trajectory assources of a possible emission; and validating one of said points as thesource of the emission.
 6. The method as claimed in claim 5, furtherincluding the step of generating another trajectory based on emissionconcentrations measured at another location, and said step of validatingcomprising taking points in agreement on both of said trajectories. 7.The method as claimed in claim 5, wherein said single measurement pointcomprises a single sensor positioned any distance from a potentialemission source.
 8. The method as claimed in claim 7, further includingthe step of superimposing a known emission concentration on said sensorduring a monitoring cycle, so that sensitivity of said sensor isenhanced.
 9. A method for determining a source of an emission, saidmethod comprising the steps of: measuring concentrations of an emissionat a single measurement point; measuring changes in wind velocity overtime; performing spatial temporal analysis of said concentrationmeasurements; generating one or more wind vectors based on said measuredchanges in wind velocity; generating two or more trajectories for theemission based on said measured emission concentrations and said windvectors; overlapping said two or more trajectories to provide an area ofoverlap; and determining the source of the emission from said overlaparea.
 10. The method as claimed in claim 9, further comprising the stepof validating said emission source in said area of overlap.
 11. Themethod as claimed in claim 9, wherein said step of measuringconcentrations of an emission comprises taking measurements from asensor that is moving to produce a plurality of measurements atdifferent locations.
 12. The method as claimed in claim 9, wherein saidstep of measuring comprises positioning a plurality of sensors in aspaced relation at locations about a facility.